Implement pushing of remote deletion

[Arthur Lutz]

When instance B is subscribed to instance A and photo X is deleted from instance A it would be nice for instance A to "notify" instance B of this deletion. This would trigger the deletion on instance B (unless instance B has modified code).

Maybe Salmon can be of use here : ​http://www.salmon-protocol.org/

source : ​http://mediagoblin.org/news/fsws-2012-wrap-up.html

[Jessica Tallon]

This will happen, not with the salmon protocol though, since this was filed the pump.io protocol has been developed we'll be using that at first and then likely progressing to ActivityPub (formally known as ActivityPump).

Not too dissimilar from the comment I left on #603, we need to implement basic federation first, once we've got media federated we will also have notifications about changes (including deletions) to media.

[Ben Sturmfels]

Closing - not useful to track federation features piecemeal. If the happen, they'll happen together.